1. Field of the Invention
This invention relates to information handling and control systems, for example for inclusion in automotive vehicle electrical systems.
In particular this invention relates to an information handling and control system comprising a central unit and a plurality of remote units each connected to the central unit by a respective signalling link, the system being operable by battery means when connected to the central unit and to at least some of the remote units, wherein the central unit includes processing and control means and power supply means therefor.
2. Description of Related Art
An example of such a system in the form of an automotive vehicle electrical system is known from the article "Multiplexing for the automotive industry" by W. R. Betts in GEC REVIEW, Vol. 2, No. 1, 1986 at pages 32 to 36.
In order to minimize current drain and conserve the capacity of the battery means in such a system it is desirable to provide for a sleep mode of the system in which the power supply means in the central unit are turned off, as well as an active mode of the system in which the power supply means are turned on to operate the processing and control means. In such a system where the user has access only to the remote units it is necessary to provide means for the user to bring the system out of its sleep mode by activation from a remote unit. For example in an automotive vehicle electrical system, it may be desirable to provide for activation from any of a number of different switches such as an ignition switch or sidelight switch which may be connected to the same remote unit, a door opening switch connected to another remote unit, and possibly a system test mode switch connected to yet another remote unit.
It is possible for the remote activation means to include a dedicated activation wire, extra to the signalling links, between the central unit and any remote unit from which the user is to be able to bring the system into its active mode. However there is a significant cost disadvantage in providing such extra activation wires together with associated connector pins and additional means for noise suppression.